Paper mills include large complex machinery to convert wood pulp into a slurry and subsequently into paper sheets. The paper sheets are wound onto large rolls that may be any size up to six feet in diameter and thirty feet long. A roll of paper produced to these dimensions may weigh up to twenty tons. Some mills may simultaneously produce plural rolls of the same or different axial lengths, with the respective rolls being disposed in generally end-to-end axial alignment. The large rolls of paper generally will be transported to another location for cutting, folding and/or printing in accordance with the intended end use of the paper.
Characteristics of the paper produced by the mill vary widely in accordance with the intended use of the paper. In particular, paper thickness, weight and surface characteristics can vary widely from one specified end use to another.
Many machines are available for testing characteristics of the paper being produced by the mill to ensure that the paper conforms to specifications. For example, available machines will employ samples of the paper being produced to test burst strength, tear strength, thickness, smoothness, gloss and other quantifiable characteristics. A prior art apparatus for determining the density of a finished roll in a mill is shown in U.S. Pat. No. 4,594,880 which issued to Murdoch et al on Jun. 17, 1986. A prior art apparatus for assessing the cross-sectional profile of the paper produced by a mill is shown in U.S. Pat. No. 4,888,983 which issued to Dunfield et al on Dec. 26, 1989. A prior art apparatus for measuring the mottle or surface gloss of paper produced by a mill is shown in U.S. Pat. No. 4,966,455 which issued to Avni et al on Oct. 30, 1990.
It is also desireable to perform non-destructive hardness tests on at least selected rolls produced by a paper mill. In particular, roll hardness observation (rho) meters are employed to test the hardness of a finished roll of paper. The typical prior art rho meter employs a hammer apparatus operatively connected to electronic means, such as an amplifier. The hammer is employed to strike the roll with a specified force, and the response of the hammer after striking the roll is measured and can be compared to specified responses indicative of the roll hardness. The prior art rho meter can be employed at selected locations along the length of the paper roll to accumulate plural readings for assessing hardness.
The prior art rho meters have been large, costly and cumbersome apparatus. Output data of the prior art rho meter has been inaccurate, and it has been difficult to properly correlate the reading taken by the prior art rho meter with the particular location on the paper being tested. Furthermore, the prior art rho meter has not been an effective tool for the anticipation or early identification of problems in the paper mill. A typical prior art rho meter is shown in U.S. Pat. No. 3,822,588 which issued Knight et al on Jul. 9, 1974.
The prior art rho meters do not enable an efficient assessment of roll hardness of paper produced by a mill. Similarly, none of the prior art rho meters provide a simple apparatus that can readily be used by workers at the mill to accurately assess hardness of a roll.
In view of the above, it is an object of the subject invention to provide a rho testing apparatus for accurately and efficiently testing the hardness of a paper roll produced by a mill.
It is another object of the subject invention to provide a rho testing apparatus that is easily transportable by workers in the paper mill.
It is another object of the subject invention to provide a rho testing apparatus and process that accurately correlates hardness data to positions on the roll being tested.
Still a further object of the subject invention is to provide a rho testing apparatus that identifies test positions independent of the speed of moving the rho tester relative to the paper.
Still an additional object of the subject invention is to provide a rho testing apparatus and process for providing the worker with usable information and summaries for assessing the performance of equipment at the paper mill over a selected period of the paper mill operation.